"Il radar olografico come nuovo metodo di indagine per la valutazione di elementi strutturali e architettonici" Lorenzo Capineri

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1 "Il radar olografico come nuovo metodo di indagine per la valutazione di elementi strutturali e architettonici" Lorenzo Capineri Laboratorio Ultrasuoni e Controlli Non Distruttivi, Dip.. Elettronica e Telecomunicazioni Università di Firenze Museo Civico di Rovereto, VII Workshop di Geofisica, 10 Dicembre 2010

2 Research topics at Laboratorio Ultrasuoni e Controlli Non Distruttivi: Ultrasound methods and instruments for Non Destructive Testing and Medical Diagnostics (since 1978) Ground Penetrating Radar (since( 1992) Infrared imaging and sensors (since 1996) A trade-off is often required among different methods!

3 Syllabus 1. Physics and Tools Holographic Radar 2. Applications Building inspection 1. Rebar in Concrete Beams 2. Radiant Heating Tubes 3. Concrete Masonry Unit (CMU) 4. Floor inspection Voids, Defects, Flaws 5. Defects and flaws in a Terracotta tiles 6. Wood Damaging Inspection Moisture 7. Brick wall texture with moisture Acknowledgements

4 Comparison of Impulse and Holographic Subsurface Radar Impulse radar Holographic radar Mixer Mixer Generator At Ar Ar At Ar Object 2 - Reference signal Object 1 - At, transmitting antenna - Ar, receiving antenna

5 Recording a Point Source Optical Holographic Interference Pattern (left). Hologram Reconstruction (right)

6 RASCAN-series radars RASCAN-4/4000, 4 GHz RASCAN-4/7000, 7 GHz RASCAN-4/ GHz

7 The Simplest Mathematical Model of Monochromatic Holographic Subsurface Radar The radar radiates electromagnetic waves at a constant frequency ω whose amplitude and phase do not depend on time. The reflected wave has constant amplitude A r, but the phase of the reflected wave φ r depends on the range to the object l ϕ = 2 r ( ε l ω Then, the reflected signal is mixed with the radar reference signal in the mixer (with A o and φ o are the amplitude and phase of the reference signal respectively). The amplitude of signal in the mixer output at the difference frequency is given by c A r A o sin(φ o - φ r )

8 Principle of Holographic radar Antenna Negative Positive Zero max max Incident Reflector Reflected

9 Characteristic appearance Antenna Positive max Zero Negative max Zero Positive max Zero Negative max To avoid blind spots holographic radar works with N discrete and programmable frequencies

10 Interference patterns (Zebra shift) A scan in air at 5 frequencies close to 4 GHz (λ= 7.5 cm) of a metal bowl with concavity up. As frequency increases Shrinks inwards

11 Holographic RASCAN-4/4000 (4GHz) radar

12 Comparison of characteristics of Impulse and Holographic Subsurface Radar Parameters Impulse Radar Holographic Radar Remarks Frequency spectrum Continuous Discrete Rascan works with 5 discrete and programmable frequencies Penetration depth Resolution at shallow depths in plan of surveying Surveying over metal substrate Possibility of object s s depth measurement Adaptation to the FCC norms Radar cost, USD Up to 10 λ 1-2 λ λ wavelength > λ 0.25 λ λ wavelength Hardly possible Directly from recorded signal Difficult 15,000-45,000 Possible? Much easier 8,000-10,000 Reverberation prevents using impulse radar over metal surface This task for holographic subsurface radar does not have a proper solution yet Frequency spectrum of holographic radar could be selected in advance. Impulse radar has a UWB spectrum that can t t be changed or limited arbitrarily

13 RASCAN scans on columns and girders

14 Instrumentation RASCAN head 4GHz with control unit Each point is sampled at 5 frequencies, from 3.6GHz to 4GHz Each point is sampled at two polarisation: cross and cocross A total of 10 images are produced Laptop with control software and USB plug Small battery

15 Site and materials Date: July, Friday Place: structures laboratory at DICEA, University of Florence Column 1/2: reinforced concrete RCK55 40x40cm 2 (property of DICEA) Girder 1: reinforced concrete SCC 30x20cm 2 without transversal bars, broken by destructive load test (property of DICEA) Girder 2: reinforced concrete RCK55/FeB44K 30x20cm 2, broken by destructive load test (property of DICEA)

16 Modus operandi A plastic mat with horizontal numbered guiding lines is fixed over the interested area The scan area size and binning is configured by using dedicated software The RASCAN head, a cylinder of about 5cm by 10cm, is manually slided along successive scan lines A double beep signals that the scan grid is completed

17 Column 1 Scan 1 Longitudinal scan, 60x30cm 2

18 Column 1 Scan 1 PARALLEL CROSS

19 Column 1 Scan 1 Column 1 Scan 1 11cm Transversal bars are over longitudinal one Clamping hole CROSS PARALLEL CROSS PARALLEL

20 Conclusions An experiment has been conducted on civil engineering structural elements, columns and girders, with the aim of detecting reinforcement bars By using RASCAN 4GHz, relative positions and mutual distances can be measured directly from the output of the device Image is easy to interpret as it reproduces a plan view of the buried structures

21 Radiant Heating Tubes Typical lay-out of heating tubes and reinforcing mesh prior to concrete pour Tubes Conduits Subsurface features accurately marked on actual the floor Radar image of unknown pipes in old concrete floor of the Russian Senate Building, Saint Petersburg scan area 1.70m х 8.04m

22 A Comparison with IR Thermal Images (warm air in tubes on a cold day) FLIR i60

23 Radiography versus IRT Radiography (X-Ray) IRT Required Access both sides one side only Radiation Hazard high none Licences or Permits yes none Set-Up Time long long (heating activated) Data Collection slow rapid Real-Time Results none complete Data Storage film digital X-Y Target Location highly accurate highly accurate Z Target Location poor to none highly accurate Target Discrimination poor to none excellent Live Line Detection none none 100% Guaranteed no no

24 Concrete Masonry Unit (CMU) Concrete blocks with dimensions about 40x24x20cm 3. The internal part of the blocks has two holes of 12.5x16cm 2 Scanning the wall by using a ruled plastic mat. Wet spots are present

25 Holographic radar scan (2 GHz) The cocross images show clearly the vertical metal bar on the left and the horizontal joint layers between concrete blocks on the right. Images 80x27 pixel, pixel size 5x20 mm 2

26 Using Holographic Radar Impulse Radar Holographic Radar Scan Area on Hospital Wall

27 Radar Scanning IR is Faster for large Walls But, must be supplemented by EMI to locate steel bars Grouted cell column FLIR i60

28 Floor Inspection at Historic Fackenthal Lecture Hall, Franklin and Marshall College, Lancaster (PA) USA Since 1787, Franklin & Marshall College has provided courses in the liberal arts and the sciences. It is one of the oldest college in USA. Fackenthal Hall is now under restoration works. The floor has been restored by using corrugated metal plates covered with about 10 cm of very old (> 40 years) concrete. Franklin & Marshall College 1910 Scan on floor surface with RASCAN 2 GHz

29 Description of Floor Bottom The corrugated metal plate was about 3cm deep and separated by 13cm. The concrete also holds rebars and conduits. CONCRETE 10cm 3cm 13 cm METAL

30 Parallel polarization Animation of Holographic Radar Images 0.5 m Cross polarization 2 m Rebars Conduit The scan is perpendicular to the corrugations. The transversal conduit is only visible by RASCAN; a 60Hz live power line detector showed no response.

31 Conclusions Holographic radar images reveal detailed information about subsurface buried objects and variations of electromagnetic properties of construction materials Multiple operating frequencies allows to distinguish overlapping objects buried within the penetration depth According to material electromagnetic properties, suitable operating frequency spectrum must be chosen within the available RASCAN radar versions (2 GHz, 4 GHz, 7 GHz)

32 Plaster void detection: comparison of IRT, X-Ray and holographic radar RASCAN method Acknowledge of RIMIDIA project rimidia.det.unifi.it (Riflettometria a Microonde per la Diagnostica dei beni Artistici)

33 Test object Flat tile filled with plaster (arriccio( arriccio). Rectangular void in the middle and a fracture on the left side (see picture). crack crack crack void fracture crack rounded corner

34 Holographic radar scans at different frequencies

35 INFRARED MEASUREMENTS The test object heated with two high power (500W) lights for 30 minutes The IR camera Mod. B60 (FLIR) with sensitivity better than 0,07 ºC C and focal plane array sensors 180x180 pixels

36 X-RAY X-RAY equipment Gilardoni (max 80kV, 3 ma ). At 50 kv for 3 minutes ( normal setting for imaging wood layers with thickness from 2 to 5 cm) the radiographic film was not imprinted By experience of X-Ray imaging of cultural heritage items (Opificio delle Pietre Dure, Firenze, Italy) the following materials are very difficult: mortar, frescos, mural wall paintings.

37 Termite Damage Losses total $1.5 billion per year in the USA alone Common in all tropical through temperate climates Termites cause the most damage in dollars, but there are many other wood-damaging damaging insects

38 Detection by Professionals Thermal imaging* Acoustic emissions Radioactive tracer bait (for ants) Inframation Institute all are non-destructive, but Find current infestations only Cannot be done during daytime for ground- dwelling nocturnal species Cannot be done during winter when insects are inactive Ole Miss Acoustics Lab *more later

39 An Ideal Detection Technology Non-destructive Should be Able to detect both active infestations and old damage Effective in any season or time of day Readily usable by structural engineers, construction workers, pest control workers, etc. Limited downtime

40 Holographic Radar Test on Boards with Known Damage Photo Radar 25 cm Tunnels visible on edge of boards only, but radar reveals internal variations also. Close-up of edge of board

41 Test on a Board with Known Damage behind Mock Wall Covering 90 x 31 cm board exposed Radar image recorded through 1 cm plasterboard

42 IRT vs. Radar 90 x 31 cm board exposed RASCAN image recorded through 1 cm plasterboard FLIR i60 image recorded through 1 cm plasterboard, with space heater behind board. Appearance of damage is transient only.

43 Radar Test on Board with Mock Damage 122 x 60 cm oak plank Tunnels mimicked by 5 mm diameter horizontal holes, drilled 12 cm lenght from edge in groupings of 1, 2, 4, and 8.

44 Radar Image of Board with Mock Damage background 8 holes 4 holes 2 holes 1 hole 88 holes clearly visible 4 and 2 progressively less so 11 hole is indistinguishable from background

45 Blind Test for Actual Damage Radar was used in a building with heavy termite damage, from an old (>10 years ago) infestation. Much damage is exposed following destructive testing and repairs. Is there hidden damage that remains undetected?

46 A Suspicious Location This double post shows no visible surficial damage, but the beams above do. Eastern subterranean termites nest in the ground, and rise into structures at night to feed. Undetected tunnels in the post would provide hidden access from the earth to the damaged beam above.

47 Radar Testing The post was scanned with RASCAN-4/4000 along lines spaced at 1 cm. The scan extended 65 cm down from the damaged beams. Scanning took less than five minutes. Results were immediate.

48 Interpreting the Radar Image Possible Damage? Fasteners? 15 cm The seam between planks

49 Damage Revealed The Radar anomaly was probed with a screwdriver, revealing hidden tunnels.

50 Another Example Damaged area eaten by termites Step guide Wooden beam Wooden floor

51 Investigation of plaster coated wall texture with holographic radar 4GHz RASCAN 4000

52 SITE DESCRIPTION The measurements have been carried out on an internal wall of a basement floor of a building built on about 1920.

53 PICTURES OF THE WALL Higher area- low moisture Lower area high moisture and delaminations The section of the original bricks (about 100 years old) has dimension 28 cm x 4 cm, separated by mortar with thickness of about 2 cm. The plaster coating has a thickness of 1.5 cm for area #1 and about 3 cm in the lower moisten area

54 SCANNED AREAS #2 #1 157 cm #3 125 cm NORTH

55 Image scans Area #1 Area #2 Polarization cross Freq_2 Scan direction horizontal 50 cm x 60 cm Pixel 1cm x 1 cm Polarization parallel Freq_2 Direction of scan vertical 50 cm x 60 cm Pixel 1cm x 1 cm

56 Image scan Area #3 Polarization cross. Freq_2 Direction of scan vertical 50 cm x 60 cm Pixel 1cm x 1 cm Real dimension of the bricks (29cm x 4 cm) Red line coincide with the height evaluated as top of the moisten area from the floor

57 Observations For the case study considered, the 4 GHz frequency is appropriate to penetrate a plaster coating with thickness from 1.5cm to 3cm The system has enough spatial resolution to reconstruct the dimension of the bricks sections and to evaluate the wall texture and eventual cavities or inhomogeneities. The texture can be observed by exploiting the two polarizations of the radar. The better situation is with parallel polarization and direction of scan perpendicular to the longest brick dimension (29 cm in our case) The presence of moisture accumulated during at least 50 years in the wall has deteriorated the plaster coating and its thickness increased from 1.5cm in the normal dry area up to 3cm in the moisten area. In several area delaminations occurred causing low penetration in the brick wall due to the plaster-air air interface Between some bricks on the sampled area were observed lack of mortar creating small cavities. Some artifacts in the images can be attributed to small (1.5 cm size) air filled cavities.

58 The author of wish to acknowledge the contribution of many collaborators of the RASCAN international team : Pierluigi Falorni,, Tim Bechtel, Sergey Ivashov, Andrey Zhuravlev, Vladimir Razevig,, Igor Vasiliev, Masharu Inagaki, Colin Windsor

59 and allpartnersofthe project Rimidia: Diagnostica non distruttiva con radar a microonde per opere d arte murarie e lignee ( finanziato dalla Regione Toscana ( )